Tripods of the character we have invented are intended to be used by surveyors and others to support instruments such as those identified above in a steady, precise orientation or alignment. Heretofore, such tripods have typically been of wooden or metallic construction. Exemplary of the heretofore proposed wooden tripods are those disclosed in U.S. Pat. Nos.: 282,182 issued July 31, 1883, to Flammang for STAND FOR PHOTOGRAPHIC CAMERAS; 588,552 issued Aug. 24, 1897, to Brownell for TRIPOD; 683,993 issued Oct. 8, 1901, to Schirber for TRIPOD OR OTHER SIMILAR STAND; and 1,863,761 issued June 21, 1932, to Neuwirth for PORTABLE SUPPORTING DEVICE. Representative, heretofore proposed tripods of metallic construction are disclosed in U.S. Pat. Nos.: 2,442,000 issued May 25, 1948, to Furnas, Jr. for TRIPOD LEG; 3,051,425 issued Aug. 28, 1962, to Homrighausen for TRIPOD WITH PLUMB; 3,589,757 issued June 29, 1971, to Mooney for AUTOMATIC LOCK FOR EXTENSIBLE CAMERA TRIPOD LEG; 3,963,207 issued June 15, 1976, to Guasti for ADJUSTABLE SUPPORT LEGS; 4,317,552 issued March 2, 1982, to Weidler for UNIVERSAL TRIPOD FOR SUPPORTING A CAMERA OR THE LIKE; and 4,453,686 issued June 12, 1984, to Ina for TRIPOD.
One of the common disadvantages of wooden tripods is that the tripod legs cannot be independently adjusted as far as their resistance to pivotable movement relative to the tripod head is concerned. Consequently, in an extreme case, one leg may be very difficult to pivot whereas another may be so loose that it will not even stay in the position to which it is pivoted. This makes the tripod awkward, and very difficult, to use; and it may even fall over and damage the instrument mounted on it.
Furthermore, metal castings are commonly employed in wooden tripods; for example, in connecting the tripod legs to its head and, if the legs are extensible, in coupling the upper and lower leg assemblies together. Typically, these castings are relatively fragile or otherwise lacking in durability. Also, because of the configurations these castings have, access to the pivot members coupling the tripod legs to the tripod head when one needs to adjust the tension between the tripod head and legs is often limited, making it difficult to effect this adjustment.
A related disadvantage is that the schemes commonly employed to connect the legs of a wooden tripod to its head involve a considerable number of components. This is a drawback from the economic viewpoint and because the coupling arrangement typically tends to loosen as the tripod is used. The resulting play between the legs and tripod head which makes it impossible for the instrument supported by the latter to be set up with the degree of precision typically required in modern, state-of-the art tripod applications.
Yet another disadvantage of wooden tripods is that their finishes are, typically, not particularly long lasting. Once the finish begins to deteriorate, water can seep into the wood. Rotting results; and, also, the wood may expand to the point where continual adjustment of the pivot members will be required. And, ultimately, the castings used in connecting the leg to the tripod head may perhaps be broken by the swelling wood.
The problems of continual adjustment and broken parts are particularly apt to occur during periodically inclement weather conditions. The wood will first swell and the moisture in it perhaps freeze, making it obviously difficult to properly adjust the tension between the leg and tripod head. Then, as the wood dries, it will shrink, perhaps loosening a tripod leg to the extent that the tripod may fall, damaging the typically expensive equipment mounted on the tripod.
Yet another weak point of the typical, heretofore available, wooden tripod is the foot. This is often a metal casting, and the area where the wooden tripod leg is connected to that casting will often rot out because of water seeping into the casting when the tripod is employed in inclement weather.
In addition, periodic tightening of the fastener holding the foot onto the tripod leg will typically be required in this wooden leg and metal foot arrangement. This progressively crushes that part of the leg in the tripod foot until, ultimately, the foot cannot be securely connected to the tripod leg. Again, this may result in enough play in the tripod leg to keep the instrument mounted on the tripod from being aimed or otherwise set up with the requisite degree of accuracy.
The metal tripods which have heretofore been available are typically copies of the earlier developed wooden tripods. Metal tripods are fabricated of an aluminum or other lightweight alloy except for those utilized to mount the surveying levels used by contractors. Those tripods are made from steel. Tripods of aluminum and similar alloys are easily dented and otherwise damaged. Both those tripods and the ones fabricated from steel have such large coefficients of thermal expansion as to typically make them unsuitable in circumstances where a high degree of precision is required because of the dimensional changes that occur as ambient temperatures vary.
In addition, rivets are commonly employed to fasten components of heretofore available metal tripods together. Riveted connections have a marked tendency to loosen. As discussed repeatedly above, this loosening is unacceptable in many applications because play between the tripod components may make it impossible to maintain an instrument mounted on the tripod in sufficiently precise alignment to be acceptable under modern day standards.
This susceptibility to denting and other damage is a disadvantage which is common to most wooden tripods because heads of wooden tripods are customarily fabricated from brass or aluminum. Damage to the tripod head may make it difficult or impossible to properly seat an instrument or to rotate or otherwise move or slide it along the instrument-supporting surface on the tripod head. And, in extreme cases, a damaged instrument supporting platform may even cause damage to the instrument itself as the latter is mounted on the tripod head.
Compounding the above-discussed drawbacks of heretofore available wooden and metal tripods are the conditions to which those tripods are commonly subjected. They are often used out-of-doors in inclement weather and not uncommonly in environments in which they are contacted by caustics, acids, and other corrosive materials. Furthermore, they are often transported over rough terrain, dropped, or otherwise subjected to handling which may damage adjustment screws or knobs or other projecting tripod components, subject wooden components to breakage, and similarly subject metal components to denting or bending. Any of these forms of damage can seriously effect the usefulness of the tripod or even make it useless, particularly in modern applications in which a high order of precision is so often required.
Another disadvantage of both wooden and metal tripods is that the bell--i.e., the fastener employed to couple an instrument to the tripod head--is not in any manner connected to the tripod. This makes it easy to lose or misplace the bell, disabling the tripod until that component can be replaced.
In addition to the disadvantages discussed above, tripods now commonly in use are difficult to adjust in height since a clamping screw or the like must be rotated to loosen the telescoping parts of each leg for adjustment. Only a small amount of corrosion or a slight bending of a screw will make it difficult to rotate. And turning a knob or thumbecrew to rotate the screw is time-consuming and can be awkward if one has only one hand free and is supporting the tripod and/or instrument being mounted on it with the other during that operation. Furthermore, clamping of the legs at a single point by a screw pin causes undesirable wear at that point.
Also, angular adjustment of prior art tripod legs is possible, but only within a limited range. This presents a problem when surrounding terrain necessitates a great range of angular position.
And, while the height and angular positions of the legs are being adjusted, smooth movement of all parts involved is desirable, but seldom possible because of the materials used, particularly as wood and metal roughen with exposure to the elements.
The lubrication of parts they require is another drawback of heretofore available tripods because this involves an added expenditure of time and money.
All in all then, the tripods typically heretofore available for supporting precision instruments such as those identified above have a number of disadvantages which make those tripods of less than optimum utility, or even totally unsuitable, for modern applications in which a high degree of precision is required.